1. Field of the Invention
The present invention relates generally to the field of radio communication networks, broadly considered, including mobile telephony networks and wireless data networks. More particularly, the present invention relates to the aspects of how mobile communication terminals, e.g. mobile phones, get connected to radio communication networks.
2. Description of the Related Art
Heterogeneous radio communication network contexts are becoming more and more common, due to the introduction of new communication technologies and standards.
An heterogeneous radio communication network context is a geographic area in which two or more different radio communication systems coexist, compliant to different standards, like for example one or more GSM (Global System for Mobile communication) systems, one or more GPRS (General Packet Radio Service) systems, one or more UMTS (Universal Mobile Telecommunication System) systems, one or more WLAN (Wireless Local Area Network) or other types of wireless data networks. The different radio communication systems may belong to a same or to different telecom service providers.
Since different radio communication systems usually differ from each other even at the lowermost layers of the communication protocol, particularly at the physical, data link, network and transport layers, an heterogeneous radio communication network context is very often a multi-RAT (Radio Access Technology) system.
Multi-mode mobile communication terminals are known in the art, and already on the market, that can work in an heterogeneous radio communication network context: for example, dual-mode mobile phones support both the UMTS and the GSM standards.
Also known in the art are reconfigurable mobile communication terminals, which, in use, can be reconfigured to change the supported radio communication standard (for example, a reconfigurable mobile communication terminal that, at a certain time, is configured to support the GSM standard, may be reconfigured to support the UMTS standard).
In an heterogeneous, or multi-RAT, context, a multi-mode and/or reconfigurable mobile communication terminal has to be able to connect to the most appropriate RAT. When turned on, the mobile communication terminal is not aware of which is the most appropriate RAT in that geographic area where it is located, or which frequency ranges the RATs existing in that specific geographic area exploit; this latter aspect is particularly critical in case DSA (Dynamic Spectrum Allocation) or FSM (Flexible Spectrum Management) techniques are implemented, because in these cases the frequency ranges of the RATs are not established a priori, being susceptible of varying in time, for example according to the network operator preferred policies. The mobile communication terminal should thus scan the entire frequency range in order to detect which are the available RATs at its current location, with a significant impact on the time required by the terminal for camping, and a great consumption of power, a resource which is precious in battery-operated hand-held devices like the mobile communication terminals.
In L. T. Le and A. H. Aghvami “Performance of an accessing and allocation scheme for download channel in SDR”, Wireless Communications and Networking Conference, Chicago, 2000, Volume 2, pages 517-521, a scheme of a communication channel called GPDCH (Global Pilot and Download CHannel) is presented, to be used for the exchange of all the broadcast and signalling messages, and for the procedures of software download for the reconfiguration of reconfigurable mobile communication terminals. The availability of a communication channel in a frequency band known a priori facilitates the task of the mobile communication terminal, which can derive from the messages sent over such a channel indications about which are the available RATs, the respective frequency bands, the different telecom operators.
In the document “Cognitive Pilot Channel” by P. Cordier et al, Wireless World Research Forum #15, 8-9 Dec. 2005, Paris, two possible solutions are presented for setting up a communication channel, the so-called “CPC” (“Cognitive Pilot Channel”), for providing sufficient information to mobile terminals, helping the connection thereof to the most appropriate network, by broadcasting relevant information with regard to frequency bands, RATs, services, load situation etc.
According to a first proposed solution, the CPC is broadcast on a wide zone including a great number of distinct meshes; the CPC contains the data for all the meshes of this area; for each mesh, the CPC contains the operators available at that mesh, their preferred technologies and the corresponding frequency bands. A terminal located in a certain mesh switches on; it determines by itself its localization, using the GPS (Global Positioning System); thanks to the knowledge of its position, the terminal is able to extract from the CPC the information on the technologies available in its mesh, the operators deploying these RATs and the corresponding frequency bands. The terminal thus establishes its connection with the relevant operator and the network.
A second solution proposed in the document of P. Cordier et al is for a CPC having a multi-level hierarchical structure, with a country level CPC (level 1), an operator level CPC (level 2) and a network level CPC (level 3). Level 1 CPC indicates who (operators) are nearby the mobile terminal region and at which frequency is the level 2 CPC being operated; level 2 CPC informs which RAT at which frequency is operated by the operator; level 3 CPC indicates the RAT information.
Similarly to the paper of P. Cordier et al. cited above, in P. Houze et al., “Common Pilot Channel for network selection”, VTC 2006-Spring, 2006 IEEE 63rd Vehicular Technology Conference, May 2006, pages 67-71, the idea to have a common pilot channel (CPC) in a harmonized frequency band to initiate the connection with the available network is described. The area covered by one broadcast channel is divided into meshes, and, for each mesh, each operator includes the corresponding information: the available technologies and the corresponding frequency bands.